With increasing down-scaling of integrated circuits and increasingly demanding requirements to speed of integrated circuits, transistors need to have higher drive currents with increasingly smaller dimensions. Fin Field-Effect Transistors (Fin FET) were thus developed. Fin FETs include vertical semiconductor fins above a substrate. The semiconductor fins are used to form source and drain regions, and channel regions between the source and drain regions. Shallow Trench Isolation (STI) regions are formed to define the semiconductor fins. The Fin FETs also include gate stacks, which are formed with sidewalls and over the top surfaces of the semiconductor fins.